Add app settings to backups

This should be compatible with Aniyomi's implementation.
Related to #1857

Co-authored-by: jmir1 <jmir1@users.noreply.github.com>

app/src/main/java/eu/kanade/presentation/more/settings/screen/SettingsBackupScreen.kt

@@ -147,6 +147,7 @@ object SettingsBackupScreen : SearchableSettings {
                 BackupConst.BACKUP_CHAPTER to R.string.chapters,
                 BackupConst.BACKUP_TRACK to R.string.track,
                 BackupConst.BACKUP_HISTORY to R.string.history,
+                BackupConst.BACKUP_APP_PREFS to R.string.app_settings,
             )
         }
         val flags = remember { choices.keys.toMutableStateList() }